Step rate tests, sometimes called formation pressure parting tests, are performed on injection wells for the purpose of determining the fracture pressure of a petroleum formation into which a fluid, usually water, is pumped through the injection well. Injection wells are located at diverse points of a formation and fluid is pumped thereinto for the purpose of driving petroleum materials in the formation toward one or more production wells through which the petroleum material may be brought to the surface, or produced. A lease pump is connected to the several injection wells through a pipe manifold so that the water pumped by the lease pump is distributed to all of the injection wells connected to the manifold to simultaneously inject the water into the formation through all of the injection wells, thereby forcing the petroleum material from the directions of all of the injection wells toward the production well or wells.
Step rate tests are performed by pumping water through the well into the formation at stepwisely increased pressure levels, the flow rate being held constant until the pressure stabilizes or becomes constant at each pressure level, or the pumping pressure being held constant at each pressure level until the flow rate becomes constant. Heretofore, the procedure has been performed in most cases by one of the following procedures.
By one procedure, which can be used only if the lease pump being used for injection has adequate pressure and flow rate capacities, the step rate test may be performed without any special equipment. The volume of fluid being pumped into the well is increased by steps, permitting pressure to become constant at each step, until the test is complete. But if the lease pump being used does not have adequate pressure and flow rate capacities, then other procedures must be used. For this procedure, injection flow to other injection wells manifold to the well being tested must be shut down in order that all of the lease pump capacity may be used for the test. Shutting down the other injection wells for a test is a time consuming and expensive procedure.
Another customary procedure is to disconnect the flow line through which water is being injected into the well, and to connect thereto a transport pump truck having its own water supply tanks and to run the step rate test by using the transport pump truck to pump water or other fluid into the well at stepwisely increased pressures until the test is completed. This, also, is a time consuming and expensive procedure. Rental of transport pump trucks is expensive, and additional tank trucks may be required to bring water to the test site.
Another procedure for accomplishing step rate tests on injection wells is accomplished by transporting a water tank to the site, filling it up with water, and then using a pump truck to pump water into the injection well at sufficiently high pressures for performance of the step rate test. This, too, is a time consuming and costly procedure.
This invention seeks to provide in a new and novel manner, methods for performing step rate tests at reduced costs and with greater efficiency, and without interruption of operations as to other injection wells.